Walkers and Tyrrells both make the same basic thing - crisps - but in very different ways. Walkers is the biggest crisp-maker in the country. Tyrrells is tiny by comparison. But success for both depend on how their crisps are made - on what happens inside the factory. Raw materials: Crisp-making at Tyrrells starts with its raw materials - the potatoes grown in fields near its factory. Tyrrells make much of their crisps being hand-made but they're...